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Interspecific hybridization plays an important role in plant evolution, contributing to taxonomic uncertainty through intermediate phenotypes or the emergence of novel traits. The characterization of hybridization is important to elucidate systematic relationships and its role in the diversification of lineages. The genus Cenostigma comprises neotropical legume trees with phylogenetic inconsistencies, and individuals showing intermediate morphology between sympatric species, suggesting natural hybridization. We tested this hypothesis by investigating two endemic species from the Caatinga dry forest in northeast Brazil (C. microphyllum and C. pyramidale) using molecular markers (nuclear and plastid SSRs), geometric morphometrics, non‐targeted metabolomics, and ecological analyses. We detected a high plastidial genetic structure among populations, not related to species boundaries but to their geographic distribution. The geometric morphometric analysis showed a clustering of pure individuals of both species with hybrids in an intermediate position, demonstrating the hybridization of these species in Caatinga. Nuclear DNA and metabolite diversity supported the separation of the two species into three clusters, with a subdivision of C. pyramidale in populations from the north (Pernambuco) and south (Bahia). Metabolomics revealed a fourth group formed mostly by hybrids. Later generation hybrids were detected as intermediate morphological forms, and gene flow was assumed as asymmetric among species and populations, being higher from C. pyramidale to C. microphyllum in populations from Bahia State. Ecological data indicated niche overlap. Hence, interspecific gene flow occurs among Cenostigma tree species, contributing to the evolution of the dry forest. Given the karyotypic and genomic similarity among species, as well as molecular and ecological evidence, we infer that the hybrids are fertile, allowing introgression and contributing to systematic complexity in Cenostigma. Hybridization did not significantly increase chemodiversity in terms of novel compounds but differentiated hybrids from parental species. In summary, we highlight the importance of multiple evidence, particularly genetic, morphological, and metabolomic traits, in the identification of hybrids and its evolutionary impact in natural environments. [ABSTRACT FROM AUTHOR]

Environmental stress is a fundamental facet of life and a significant driver of natural selection in the wild. Gene expression diversity may facilitate adaptation to environmental changes, without necessary genetic change, but its role in adaptive divergence remains largely understudied in Neotropical systems. In Amazonian riparian forests, species distribution is predominantly influenced by species' waterlogging tolerance. The flooding gradient delineates distinct wetland forest types, shaping habitats and species characteristics. Here we investigated the molecular basis of environmental stress response in a tropical ground-herb species (Ischnosiphon puberulus) to environmental variation in Amazonian riparian forests. We compared environmental variables and gene expression profiles from individuals collected in two forest types: Igapó and Terra firme in the Amazonian riparian forests. Predictable seasonal flooding poses a significant challenge in Igapó compared to Terra firme environments, with the former presenting higher water column height and longer flooding duration. Our findings suggest that contrasting environmental conditions related to flooding regimes are important drivers of population genetic differentiation and differential gene expression in I. puberulus. Enriched gene ontology terms highlight associations with environmental stresses, such as defence response, water transport, phosphorylation, root development, response to auxin, salicylic acid and oxidative stress. By uncovering key environmental stress response pathways conserved across populations, I. puberulus offers novel genetic insights into the molecular basis of plant reactions to environmental constraints found in flooded areas of this highly biodiverse neotropical ecosystem., (© 2024 John Wiley & Sons Ltd.)

Ameroglossum is a rare plant genus endemic to northeastern of Brazil, initially monospecific (A. pernambucense) and recently expanded by the description of eight new species and two related genera. The genus was initially placed in the family Scrophulariaceae, but this has never been phylogenetically tested. This group is ecologically restricted to rocky inselberg habitats that function as island-like systems (ILS) with spatial fragmentation, limited area, environmental heterogeneity, temporal isolation and low connectivity. Here we use a phylogenetic perspective to test the hypothesis that Ameroglossum diversification was related to island-like radiation in inselbergs. Our results support that Ameroglossum is monophyletic only with the inclusion of Catimbaua and Isabelcristinia (named here as Ameroglossum sensu lato) and this group was well-supported in the family Linderniaceae. Biogeographic analyses suggest that the ancestral of Ameroglossum and related genus arrived in South America c.a. 15 million years ago by long-distance dispersal, given the ancestral distribution of Linderniaceae in Africa. In rocky outcrop habitats, Ameroglossum s.l. developed floral morphological specialization associated with pollinating hummingbirds, compatible with an island-like model. However, no increase in speciation rate was detected, which may be related to high extinction rates and/or slow diversification rate in this ecologically restrictive environment. Altogether, in Ameroglossum key innovations involving flowers seem to have offered opportunities for evolution of greater phenotypic diversity and occupation of new niches in rocky outcrop environments., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)